Among the manifold habits shown by calcite, that of the combination of the base c{0001} with a rhombohedron, yielding an eight-sided solid, is not common. Out of 2544 combinations illustrated in Goldschmidt's Atlas der Kristalformen,1 only 26 show only the base and a rhombohedron. If the angle (0001) (h0hl) is close to 70°, and if the intersection of opposite faces is a point and not a line, then every face is a triangle and the crystal closely resembles an octahedron.

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